1. Field of the Invention
The present invention relates to a non-contact/contact integrated type of a capacitance sensor for detecting an object's such as a human body nearing or contacting a door and the like of a vehicle.
2. Description of the Related Art
Conventionally, it is known a pinch prevention apparatus that prevents a hand(s) and a finger(s) from being pinched between a movable part of a vehicle such as an automatic open/close power sliding door and power window and a holding part thereof such as a center pillar and window frame for receiving the movable part (for example, see paragraphs 0002 to 0026 and FIG. 1 in Japanese Patent Laid-Open Publication No. 2001-32628). The pinch prevention apparatus is equipped with a capacitance sensor for detecting a human body and is designed to stop the movable part according to a human body detection signal detected by the capacitance sensor or to move the movable part to an opposite direction.
Generally, as shown in FIG. 9A, a capacitance sensor is equipped with a detection electrode E1, a grounding electrode E2, an insulator In pinched between the detection electrode E1 and the grounding electrode E2, and a coating member consisting of an insulation material arranged so as to surround a periphery of the detection electrodes E1 and E2 and the insulator In. And the capacitance sensor is arranged, for example, on an end face at a side of a movable part facing a holding part.
In such the capacitance sensor, as shown in FIG. 9B, an electric charge is supplied to the detection electrode E1 from an electric charge supply circuit through a pulse generation circuit and an output amp. That is, because the detection electrode E1 and the grounding electrode E2 configure a capacitor, an electric potential V output through the detection amp is expressed in a following formula (1):V=Q/(C1+C2),  (1)where Q represents an electric charge charged in an capacitance sensor (capacitor), C1 represents a capacitance of the capacitance sensor itself, and C2 represents a capacitance, stray capacitance between the capacitance sensor and the ground.
And if a human body nears the capacitance sensor, the electric potential V changes according to a capacitance between the capacitance sensor and the human body. That is, the electric potential V is expressed in a following formula (2):V=Q/(C1+C2+C3),  (2)where Q, C1, and C2 are same as in the formula (1), and C3 represents a capacitance between a human body and a capacitance sensor.
Accordingly, the more the human body nears the capacitance sensor the more the C3 augments, and resultingly, the electric potential V output through the detection amp becomes smaller and smaller. In other words, the capacitance sensor is designed to detect the human body according to the change of such the electric potential V.
In this connection, as shown in FIG. 9C, in such the capacitance sensor there is a case that a droplet W adheres to peripheries of the detection electrode E1 and the grounding electrode E2, for example, to the coating member due to rainfall and the like. Because if the droplet W thus adheres to the coating member, the capacitance sensor has the grounding electrode E2, a capacitance thereof increases in an increment of a capacitance Cw of the droplet W.
However, if the capacitance Cw of the capacitance sensor increases, it lowers output of the electric potential V as if a human body nears the capacitance sensor. Accordingly, the pinch prevention apparatus using such the capacitance sensor results in malfunctioning by a disturbance due to the adherence of the droplet W.
Consequently, it is strongly requested a novel non-contact/contact integrated type of a capacitance sensor that can prevent a malfunction by a disturbance due to the adherence of a droplet and the like, can perform an accurate detection when an object such as a human being nears a door and the like of a vehicle, and can surely detect the object also when it directly contacts the door and the like.